docs: def close(self):
          """
          Closes the underlying socket of the PB connection.
          """
          if self._socket:
              if USE_STDLIB_SSL:
                  # NB: Python 2.7.8 and earlier does not have a compatible
                  # shutdown() method due to the SSL lib
                  try:
                      self._socket.shutdown(socket.SHUT_RDWR)
                  except EnvironmentError:
                      # NB: sometimes these exceptions are raised if the initial
                      # connection didn't succeed correctly, or if shutdown() is
                      # called after the connection dies
                      logging.debug('Exception occurred while shutting '
                                    'down socket.', exc_info=True)
              self._socket.close()
              del self._socket